- 1.7 tballast per m³ at 1:5
- 69× 25kg bags per m³
- 2 + 1bulk bags + one small bag
- 14 bagsof cement with it
Ballast per cubic metre by mix
Per m³ of finished concrete, no waste added (add 5–10% for your job).
| Mix | Ballast | 25kg bags | 850kg bulk bags | Cement (25kg) |
|---|---|---|---|---|
| 1:4 (driveways) | 1.64 t | 66 | 2 (just enough) | 17 |
| 1:5 (slabs, bases) | 1.71 t | 69 | 2 + one 25kg bag | 14 |
| 1:6 (footings) | 1.76 t | 71 | 2 + three 25kg bags | 12 |
Half a cubic metre needs half as much: about one bulk bag (or 33–36 small bags) and 6–9 bags of cement.
Two 850kg bulk bags fall a few kilos short of a full m³ at 1:5, so the concrete calculator rounds up to a third bag. In practice a 25kg bag tops it up, or you allow a little waste.
The sum
Dry materials ≈ 2,050kg per m³
Ballast = 2,050 − 2,050 ÷ (mix parts + 1) e.g. 1:5 → 2,050 − 342 = 1,708kg
25kg bags = 1,708 ÷ 25 = 69
